Small Craft Advisory 33, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
452 AM CDT Sun Apr 19 2020

.SYNOPSIS...

Surface analysis showed a retreating 1017mb high over Virginia. A
1014mb low was located off the coast of South Carolina with
associated boundary/warm front extending west to southern
Mississippi to southeast Texas. In addition, our next
system/1003mb surface low was over Texas Panhandle. Southeast
winds were present over the forecast area this morning.

Upper air analysis showed a positively titled trough axis from
western Kansas to New Mexico and another disturbance over Oregon.
Wind flow over the southern tier CONUS was west to southwest but
this will change with approaching systems. Isotach analysis at 250mb
showed the sub-tropical jet from Baja California to south Texas
and the jet stream cradling the disturbance from southern Nevada
to west Texas to the Mid Mississippi Valley.

&&

.DISCUSSION...

Positively tilted trough over the Central Plains will track east
today becoming neutrally tilted from southeast Missouri to north
Louisiana. At the same time, the surface low over Texas Panhandle
will track east to Georgia by midnight tonight.

Mean relative humidity values approach to 100 percent mainly
north I-12. However, precipitable water value of 1.8 inches was
pooling along and south of the warm front...mainly over the
forecast area this morning. As the trough axis and surface low
sweeps east, higher PW values 1.8 to 2.0 will pool along warm
front over north Louisiana and central Mississippi and more
pooling in warm sector over part of the forecast area this
afternoon. Surface base cape values will increase to 2000 to 2500
j/kg over northwest zones...mainly northwest of Lake
Pontchartrain. At the same time, low level flow will increase with
boundary layer winds 25 to 30 knots over southwest Mississippi.
With nose of the sub-tropical jet max approaching, 0-3km helicity
values of 200 to 250m/s across the south half of the forecast area
and 250 to 325m/s across the north half this afternoon...shifting
east through the evening. Lapse rates from 700 to 500mb becomes
steep along the frontal push with rates 7.0 to 7.5C/km.

All these parameters equate to isolated tornadoes, damaging winds
and hail threats possible across the forecast area with a
slightly higher threat across the north half of forecast this
afternoon and this evening.

Dry weather and near normal temps are expected next week to mid
week. Another system will bring another chance of spring storms
across the forecast area Thursday. This system will likely take a
more northerly track but possibly bringing a threat of strong
storms across the forecast area on Thursday.

&&

.AVIATION...
Main concern will be low clouds that envelop the area
through the morning. Overall most terminals will drop to IFR
status with BKN or OVC around 800 but a few sites may fall to
LIFR around 300 ft. Some reductions in vsbys are possible however
not anticipating many terminals dropping below 3sm. Conditions
should begin to improve a few hours after sunrise and then
convection most taf sites between 20z today and 05z monday from
east to west.

&&

.MARINE...

Small Craft Advisories are in effect for all marine zones for this
morning through early Monday morning. Wind shift takes place with
cold frontal passage late tonight for mostly WNW flow that veers
over time to easterly by Tuesday morning then SE Tuesday evening.
SCA conditions are likely to arise once again Wednesday in advance
of developing strong storm system in the Plains States that
tightens the pressure gradient over the gulf coast region. 18

&&

.DECISION SUPPORT...
DSS code: ORANGE.
Activities: Forecast support for IDSS critical locations
            River Flood Warnings for MS River
            Assessing severe weather threat for Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  82  62  78  57 /  60  60   0   0
BTR  84  63  78  57 /  40  40   0   0
ASD  86  64  82  59 /  40  60   0   0
MSY  85  68  81  64 /  20  20   0   0
GPT  81  66  80  60 /  40  60   0   0
PQL  82  65  83  58 /  40  60   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Wind Advisory from noon today to 11 PM CDT this evening for
     LAZ034>037-039-040-046>050-056>072.

GM...Small Craft Advisory from 7 AM this morning to 7 AM CDT Monday
     for GMZ530-532-534-536-538-550-552-555-557-570-572-575-577.

MS...Wind Advisory from noon today to 11 PM CDT this evening for
     MSZ068>071-077-080>082.

GM...Small Craft Advisory from 7 AM this morning to 7 AM CDT Monday
     for GMZ532-534-536-538-550-552-555-557-570-572-575-577.

&&